1. Field of the Invention
The invention relates generally to systems and methods for detecting the presence or absence of a variety of analytes in a fluid sample using a diagnostic instrument, and, in particular, for determining diagnostic test results by image analysis of a digital image of the diagnostic instrument.
2. Description of Related Art
Reagent dipsticks and immunoassays have been used in medical clinics for decades in connection with methods for rapidly diagnosing health conditions at the point of care. In a clinical environment, dipsticks have been used for the diagnosis of urinary tract infections, preeclampsia, proteinuria, dehydration, diabetes, internal bleeding and liver problems. As is known, dipsticks are laminated sheets of paper containing reagents that change color when exposed to an analyte solution. Each reagent test pad on the dipstick is chemically treated with a compound that is known to change color in the presence of particular reactants. For example in the context of urinalysis, the dipstick will typically include reagent pads for detecting or measuring analytes present in a biological sample such as urine, including glucose, bilirubin, ketones, specific gravity, blood, pH, protein, urobilirubin, nitrite, leukocytes, microalbumin and creatinin.
The magnitude of this color change is proportional to analyte concentration in the patient fluid. Dipsticks are typically interpreted with the naked eye by comparing the test strip against a colored reference chart. However, such color comparison can cause user confusion and error, for several reasons including changes in ambient lighting, and that a significant portion of the population has impaired color vision.
Automatic methods and apparatus for interpreting test results of dipsticks and immunoassays, which have been exposed to a sample solution, are known in the art. For example, U.S. Patent Application Publication No. 2012/0063652 to Chen et. al (hereinafter “the '652 publication”) discloses a method for color-based reaction testing of biological materials, albeit in an un-calibrated environment, by capturing a digital image of both a test strip and a colored reference chart side by side in a single image. The test results for the test strip are automatically obtained by performing simple color matching between the reacted regions of the test strip and the color reference chart to determine analyte concentration of the biological material.
When employing the method disclosed by the '652 publication, a user must properly align the test strip and the color reference chart before capturing the digital image. Therefore, a user must come into contact with the exposed test strip, after it is soiled by biological samples, such as urine, blood, or feces, and place it in an appropriate position relative to the color reference chart. Therefore, to assist in placement of the test strip and/or chart, automatic interpretation apparatus often include an additional positioning element, such as a box or carpet, to position both the test strips and the chart in the correct orientation.
In view of the problems with presentably available methods for automatically reading test strips, there is a need for an automated testing method, which uses a digital image captured in an un-calibrated environment. The system or method should be configured to automatically calibrate the digital image to correct any color deficiencies, artifacts, or other ambiguities. The method should also automatically identify the relevant portions of the digital image, regardless of how the test strip and/or color reference are positioned in the digital image. Finally, the method should minimize manipulation of samples soiled with biological fluids. The presently invented method and system address these deficiencies of known automatic detection devices, systems, and methods.